Significance The development of an effective contraceptive vaccine could be useful in countries where medical care is limited. Objectives In this study, the sperm antigen hT-CAST, a synthetic peptide that contains the B-cell epitope of the sperm specific isoform of Calpastatin will be formulated with Squalene-Arlacel A 3:1 as the vehicle, to be given to adult females that are reproductively healthy as determined by specific criteria. Results Animals must be at least five years old, cycling regularly and have a normal screening ultrasound examination of their reproductive tracts to check for any physical abnormalities. A treatment and control group consisting of 15 females per group will receive either 300 5g of hT-CAST (treated) on study days 0, 28 and 84, or vehicle (control) only on study days 0, 28 and 84. Each treatment will consist of two intramuscular injections in each animals' outer thighs. Blood will be collected once prior to treatment, then once per week throughout the 12 week treatment period. Blood samples will be processed for serum, heated to decomplement the antibodies being measured, then sent to Dr. Goldberg for antibody titer analysis. Timed matings will be scheduled at a minimum of 3 weeks post third treatment, timed to each animals' respective menstrual cycle. There will be four consecutive menstrual cycle breedings per animal scheduled, with three breedings per cycle. Animals will be r emoved from breeding schedule upon pregnancy confirmation. If the pregnancy rate is reduced by the vaccine, one cycle of daily urine samples will be analyzed for ovarian steroids to confirm normal ovarian function. Future Directions The animal use protocol has been approved and animals are being screened for assignment to the study. KEY WORDS immuno-contraception, sperm antigens, vaccine FUNDING NIH Grant HD-6-3247